1. Technical Field
This invention relates to electric induction heating coils for heating metal billets that provide “high” point of use temperature within a limited area. Such induction heating coils require that the conductive coil “winding” be surrounded with a water cooled corresponding coil and an insulation layer to keep the “winding” at the desired operational temperature.
2. Description of Prior Art
Prior art insulation applications heretofore use the best available high temperature resistant insulation materials having the physical properties required for relative thin layer shaped conforming applications, such as asbestos. As has been well documented, asbestos mineral fibers are hazardous when they become friable, inhaled or exposed to the human organism. Insulation lining of vessels is well known, see U.S. Pat. Nos. 4,241,843 and 4,313,400 as well as novel induction heating apparatus coils, see U.S. Pat. No. 6,730,893 which illustrates prior art induction heating coils in which a magnetic field is generated by the coil and passes through the object to be heated. Prior art induction coil isolation insulation is used to protect the inductive coil, (winding) from the high temperatures induced in the metal billet during the heating cycle and contact with a conductive liner. Aluminum billets which are typically extruded offer operational challenges due to the low conductivity values associated with non-ferrous metals. Given that asbestos insulating liners of the coil surface has been the standard, the required replacement with less performing material has been the only option such as glass cloth. Such replacement materials have a shortened effective operational life especially in the so-called “gap” formed by the typical stainless steal induction coil liner which cannot be continuous in this electro-magnetic environment. The gap in the stainless steel liner becomes a critical failure point of new replacement materials and thus, as noted, shortens the overall usefulness and service life of the insulation before replacement. Such insulation within the gap becomes burned, brittle and fractured during use and must be replaced or the liner will short out the coil and fail.